Production of stabilized dispersions of color couplers for photographic materials



United States Patent PRODUCTION OF STABILIZED DISPERSIONS 0F COLOR COUPLERS FOR PHOTOGRAPHIC MA- TERIALS Gerald Noel White, Carshalton, Surrey, England, assignor to The Pavelle Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Mar. 23, 1962, Ser. No. 182,097

' 14 Claims. (Cl. 96100) This invention is concerned with improvements in or relating to the production of photographic emulsions and more particularly with the production of improved dispersions, suspensions or colloidal solutions of color couplers in a photographic dispersion medium such as gelatine. v The incorporation of color coupler compounds, into silver halide emulsion has always presented difiiculties. One known method consists of dissolving the color coupler compound in aqueous or aqueous alcoholic alkali, the coupler compound having been provided in the course of its synthesis with acidic groups to give it this solubility. The addition of a highly alkaline solution to the silver halide emulsion followed by the precipitation of the free coupler on correction to an acid pH however, gives rise to many undesirable effects on both the photographic characteristics and the physical properties of the emulsion. There is, for instance, no check on the particle size of the precipitated coupler on which the speed of coupling, and therefore, also the efficiency of coupling depends. The separation of the precipitated coupler, moreover, is not immediate but may take place during coating leading to variations in viscosity and, if this is not corrected, to increases in coating thickness. As -a result, the values for speed, contrast, grain size and viscosity of a black and white emulsion are adversely affected by the addition of a highly alkaline coupler solution and are not restored on subsequent acidification.

Because of these disadvantages attempts have been made to make dispersions of color couplers which are neutral or slightly acid and of true colloidal character. There is, however, a tendency for dispersions produced by the action of the anionic wetting agents to undergo an increase in particle size on storage with consequent variation of coupling efficiency and coating viscosity,

It is an object of the present invention to provide an improved method of preparing dispersions of color couplers in a photographic dispersion medium,

I have found that neutral or slightly acidic dispersions of color couplers in a dispersion medium of true colloidal character and having improved stability can be produced by preparing a dispersion of a salt of a color coupler in a dispersion medium containing an anionic wetting agent and a glycol and effecting the acidification of the dispersion in the set condition.

According to the invention, therefore, I provide a process 'forthe preparation of improved neutral or acidic dispersions of color couplers in a dispersion medium in which a salt of the color coupler is dissolved in an aqueous dispersion of a dispersion on medium-containing a glycol and an anionic wetting agent, the dispersion being then allowed to set and thereafter treated with acid to render the dispersion neutral or acid.

Preferably the set dispersion is brought to a pH of from 56.5 by the treatment with acid.

The photographic dispersion medium used in the process according to this invention may be of the types generally used in the preparation of photographic emulsions, a particularly satisfactory substance being gelatine; other suitable substances include polyvinyl-alcohol, car-boxymethylcellulose and polyvinylpyrollidone.

The color coupler used is of an acidic nature having a carboxyl or sulphonic group, preferred couplers being those having a fatty acid group containing not less than 8 carbon atoms. Suitable color couplers are, for example, 6-sulphonyl-1-hydroxy-2-N-stearyl naphthoic amide (Cyan) 3 -sulphonyl-4-phenoxyphenyl-3 -stearyl-5-pyrazolone (magenta) and 4-1aurylamino-benzoyl-acetyl-3- aminoisophthalic acid (yellow). Other color couplers which can be used with particular advantage are those described in copending application Ser. No. 182,082, filed Mar. 23, 1962.

The color coupler is used in the form of a water soluble salt, salts with organic bases such as triethanolamine being preferred. Other suitable organic bases include benzylamine and triethylamine.

The anionic wetting agent is preferably a salt of an aryl or ali'cyclic amine with sulphated lauryl alcohol, for example cyclohexylamine lauryl sulphate or benzylamine lauryl sulphate.

The glycol is preferably one containing from two to six carbon atoms but preferably having three carbon atoms in a straight chain between each hydroxyl group. Hexylene glycol (2-methylpentan-2, 4-diol) is particularly satisfactory.

I now describe for the purpose of illustration only one convenient general method for the preparation of the improved coupler dispersions according to the invcntion.

An aqueous dispersion of the dispersion medium is first prepared by heating as necessary and the anionic wetting agent added. An aqueous solution of the salt of the color coupler and the glycol is next prepared. The coupler salt may be added as such or alternatively the free acid can be dissolved in water containing the desired base. If desired, a Water miscible organic solvent, e.g., methanol or ethanol may be added to insure that a clear solution is obtained. The coupler solution and the aqueous dispersion of the dispersion medium are then combined and the whole allowed to set. The set dispersion is then shredded and the shreds treated with acid, e.g., by immersion or rinsing with aqueous acid until the desired pH is attained. The pH of the shreds can be determined by melting a rinsed shred and measuring the pH of the resulting liquid dispersion, e.g., with a suitable pH meter. An inorganic or organic acid may be used for the acidification, acetic acid, citric acid or tartaric acid being preferred. When the pH of the shreds has reached the desired value they are washed with water, drained or centrifuged and are then ready for use.

I have found that photographic emulsions into which coupler dispersions prepared according to the invention have been incorporated in general remain substantially constant in viscosity for at least 2 days and without change in contrast show a noticeable gain in speed. I have further found that the set coupler dispersion shown substantially no alteration in particle size, pH or properties in usage rafter storage for 2 months. Moreover, dispersions made in accordance with the invention are substantially optically transparent and do not in general reduce the resolution characteristic of the light sensitive emulsion to which they are added. In cases in which the addition of the coupler in alkaline solution to the photographic emulsion has, even after pH adjustment with acid, caused a heavy drop in the speed of development, I have found that the addition of the coupler in the form of a dispersion prepared according to the invention has left the development speed of the emulsion unaffected.

For a better understanding of the invention the following example is given by way of illustration only:

Example 5 kg. of Inert Gelatine were melted with mild agitation in 40 litres of distilled water with the addition of 50 grams of cyclohexylamine lauryl sulphate at a temperature of about 75 C. To this solution was added with continued mil-d agitation a solution made up by dissolving 1.0 kg. of the aforementioned cyan coupler in a mixture of 2.8 litres of ethanol and 2.8 litres of hexylene glycol followed by the addition of sufficient 20% aqueous triethanolamine to bring the coupler into complete solution at 75 C, At this temperature the coupler solution was added with agitation to the gelatine dispersion which was then set as rapidly as convenient and shredded. The shreds were then immersed in about 30 litres of water to which had been added 1.5 litres of 10% acetic acid. After one hour a shred was removed, rinsed and melted. If it is found to have a pH greater than 6.5 immersion is continued until this pH is observed in melting a rinsed shred. The shreds were then washed in running water for 3 hours, remelted, filtered through cloth and finally set for storage, or for addition as shreds to a photographic emulsion.

Iclaim:

1. A method of preparing stable colloidal color coupler dispersions for incorporation into photographic silver halide emulsions comprising preparing a dispersion of a water soluble basic salt of a color coupler in an aqueous dispersion medium containing an anionic wetting agent and an aliphatic glycol containing from three to six carbon atoms as a stabilizing agent, allowing said dispersion to set, and treating said set dispersion with an acid to render said dispersion at least neutral.

2. A method according to claim 1 wherein said set dispersion is brought to a pH of from 5 to 6.5 by treatment with an acid.

3. A method according to claim 1 wherein said dispersion medium is gelatine.

4. A method according to claim 1 wherein said color coupler has a fatty acid group containing not less than 8 carbon atoms.

5. A method according to claim 4 wherein said color coupler is in the form of a water soluble salt of an organic base.

6. A method according to claim 1 wherein said anionic wetting agent is a salt selected from the group consisting or aryl amine and alicyclic amine with sulphated lauryl alcohol.

7. A method according to claim 1 wherein said color coupler is selected from the group consisting of 6-sulphonyl-l-hydroxy-2-N-stearyl naphthoic amide, 3-sulphonyl-4-phenoxy-phenyl-3-stearyl-5-pyrazolone, and 4- lauryl-aminobenzoyl-acetyl-3-aminoisophthalic acid.

8. A method according to claim 7 wherein said color coupler is in the form of a salt of a triethanolamine base.

9. A method according to claim 1 wherein said anionic wetting agent is cyclohexylamine lauryl sulphate.

10. A method according to claim 1 wherein said anionic wetting agent is benzylamine lauryl sulphate.

11. A method according to claim 1 wherein said glycol has 3 carbon atoms in a straight chain between each hydroxyl group.

12. A method according to claim 11 wherein said glycol is hexylene glycol.

13. A color coupler dispersion for photographic emulsions formed by the method of claim 1. p

14. A method of producing color photographic emulsions which comprises dispersing a basic water soluble salt of a color coupler in an aqueous dispersion medium containing an anionic wet-ting agent and an aliphatic glycol containing from three to six carbon atoms as dispersion and stabilizing agents under conditions controlled to prevent the precipitation of the dispersion medium, allowing the dispersion to set, shredding and treating the shredded set dispersion with acid to render the dispersion at least neutral washing the acid-treated dispersion and blending the shreds into a silver halide photographic emulsion.

References Cited UNITED STATES PATENTS 2,186,717 l/1940 Eggert et al. 96l00 2,310,226 2/1943 Gasper 96-100 2,527,261 10/1950 Hart et a1 96-100 2,577,127 12/1951 Jennings et al 96100 2,801,171 7/1957 Fierke et al. 96---100 3,056,674 10/1962 Hoffstadt et al 96100 NORMAN G. TORCHIN, Primary Examiner.

LOUIS P. QUAST, Examiner,

J. T. BROWN, Assistant Examiner. 

1. A METHOD OF PREPARING STABLE COLLOIDAL COLOR COUPLER DISPERSIONS FOR INCORPORATION INTO PHOTOGRAPHIC SILVER HALIDE EMULSIONS COMPRISING PREPARING A DISPERSION OF A WATER SOLUBLE BASIC SALT OF A COLOR COUPLER IN AN AQUEOUS DISPERSION MEDIUM CONTAINING AN ANIONIC WETTING AGENT AND AN ALIPHATIC GLYCOL CONTAINING FROM THREE TO SIX CARBON ATOMS AS A STABILIZING AGENT, ALLOWING SAID DISPERSION TO SET, AND TREATING SAID SET DISPERSION WITH AN ACID TO RENDER SAID DISPERSION AT LEAST NEUTRAL. 